Although liver diseases are uncommon in dogs, one of its most common forms is chronic hepatitis (CH). CH is a histologic diagnosis, characterised by the presence of fibrosis, inflammation, and hepatocellular apoptosis and necrosis. Cirrhosis can result as the end stage of the disease. One of the causes of CH is hepatic copper accumulation. Hepatic copper accumulation can result from increased uptake of copper, a primary metabolic defect in hepatic copper metabolism, or from altered biliary excretion of copper. In the latter case, copper toxicity is secondary to hepatic inflammation, fibrosis, and cholestasis, although it is unclear to what extent this occurs in the dog. In secondary copper storage disease, copper accumulation is mainly restricted to periportal parenchyma and hepatic copper concentrations are lower than accumulation in familial storage diseases. Whilst, the nature of the initiating factor(s) and of the sensitizing antigen is unknown, immunological abnormalities and morphologic features observed in primary biliary cirrhosis are concurrent with an immune mediated mechanism.
The small intestine is recognized as the main site of dietary copper absorption in mammals. Transport from the intestinal lumen into intestinal mucosa is a carrier-mediated process involving a saturable transport component. Once in mucosal cells, approximately 80% of the newly absorbed copper is in the cytosol, mainly bound to metallothioneins (MT). These are low molecular weight inducible proteins with many functions including homeostasis, storage, transport and detoxification of metals. After passage through the enterocytes, copper enters the portal circulation where it is bound to carrier proteins peptides and amino acids and is transported to the liver with lesser amounts entering the kidney. In most mammals, copper is excreted easily, and the main route of excretion of copper is the bile.
The genetic basis for hepatic copper accumulation is unknown. This is made difficult by the fact that copper is involved in numerous different biological pathways, each of which is highly complex and involves a large number of genes. Dogs with excessive hepatic copper accumulation are typically treated with D-penicillamine, a potent copper chelator. Ultimately however, the most successful treatment available for dogs with CH is liver transplantation.
WO 2009/044152 A2 discloses a method of determining the susceptibility of a dog to liver copper accumulation comprising detecting the presence or absence of (a) a polymorphism in the GOLGA5, ATP7a or UBL5 gene of the dog that is indicative of susceptibility to copper accumulation and/or (b) a polymorphism in linkage disequilibrium with a said polymorphism (a), and thereby determining the susceptibility of the dog to liver copper accumulation. International application no. PCT/GB09/02355 (not yet published) discloses further polymorphisms for use in a method of determining the susceptibility of a dog to liver copper accumulation.